Re: [RFC/PATCH 1/4] sched: remove isolcpus

From: Max Krasnyanskiy
Date: Wed Feb 27 2008 - 18:57:34 EST


Peter Zijlstra wrote:

cpu isolation doesn't offer anything over cpusets, hence remove it.

Works for me. That's what I suggested in my reply to your comments.
Here is the quote from the previous thread:

This also allows for isolated groups, there are good reasons to isolate groups,
esp. now that we have a stronger RT balancer. SMP and hard RT are not
exclusive. A design that does not take that into account is too rigid.

You're thinking scheduling only. Paul had the same confusion ;-)

I'm not, I'm thinking it ought to allow for it.
One way I can think of how to support groups and allow for RT balancer is this: Make scheduler ignore cpu_isolated_map and give cpusets full control of the scheduler domains. Use cpu_isolated_map to only for hw irq and other kernel sub-systems. That way cpusets could mark cpus in the group as isolated to get rid of the kernel activity and build sched domain such that tasks get balanced in it.
The thing I do not like about it is that there is no way to boot the system with CPU N isolated from the beginning. Also dynamic isolation currently relies on the cpu hotplug to clear pending irqs, softirqs, kernel timers and threads. So cpusets would have to simulate the cpu hotplug event I guess.

Max

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